Coupling circuit



Nov, 26, 1946. B, WAT-rs, JR 2,411,564

COUPLING CIRCUIT Filed July 4. 1942 I ,LI FIG 1 a? HEGH FREQUENCY souncs HIGH FREQUENCY $0URCE HIGH FREQUENCY SOURCE HIGH FREQUENCY SOURCE INVENTOR BYG-IESTER WATTS #2 ATTORNEY Patented Nov. 26, 1946 I UNITEDSTATES PATENT OFFICE COUPLING CIRCUIT Chester B. Watts, Jr., East orange, N. .l'., assignor to Federal Telephone and Radio Corporation, a corporation of Delaware Application July 4, 1942, Serial No. 449,828

9 Claims.

One of the most practical schemes forimpedance matching heretofore proposed is the adjustable short circuited stub-line type of transformer. Each such stub-line used, however, requires two adjustments; one being the location of the stubline with respect to either the maximum or minimum voltage points of the transmission line, de-

pending upon whether step-up or step-down matching is desired,'and the other, an adjustment lengthwise of the stub-lineof the shortcircuiting conductor thereof. This type of transformer can be used with a fair degree of satisfaction for impedance matching of simple networks such as two transmission lines. However, when complex network arrangements are concerned such, for example, as when aplurality of loads are to be matched to a transmission line having a single source of high frequency energy thereby requiring two or more stub-line transformers, it is exceedingly difilcult to reach an impedance balance. This is because each stubline has two adjustments, and any network requiring more than one transformer will require twice the number of adjustments as there are transformers, and since the adjustment of each transformer alters the impedance matching characteristics of each of the others, it is almost a hopeless task to properly match by means of stubline transformers a complex network system.

One of the objects of this invention, therefore, is to provide an impedance matching transformer having but a single adjustment.

Another object of the invention is to provide an impedance matching transformer which may be readily arranged for step-up or step-down impedance matching.

Still another object of the invention is'to provide impedance matching transformers for effective impedance matching of a single or plural load and/or a single or plural source of high frequency ener y- The above and other objects of this invention i I accomplish by combining a short circuited stubline and an open circuited stub-line conductively connected together by an adjustable connection so as to vary in inverse relation the efi'ective lengths of the two stub-lines. More particularly, the short circuited stub-line may comprise two parallel spaced apart conductors having one end thereof short circuited and the other end connected to a common junction or other point in one of the networksat which impedance matching is desired, Assuming that the adjustable connection has substantially the same surge impcdance as the stub-lines, the length of the short circuited stub-line may be chosen in the order of a quarter wavelength should a step-up transformation be required, or in the order of a half wavelength should a step-down transformation be desired. If additional lengths are required between the location of the transformers and the points in the network to which it is to be connected, additional lengths may be added thereto in the order of a half wavelength and multiples thereof, for either quarter wave or half wavelength stubs.

In either a step-up or a step-down transformer, the open circuited stub-line thereof is taken substantially as a quarter wavelength and may comprise two parallel conductors arranged in spaced relation with respect to the parallel conductors of the short circuited stub-line. I find that when the overlap between the two lines, or the distance provided for movement of the adjustable connection, is slightly less than a quarterwavelength, that is to say, about two-tenths of a wavelength, more or less, the maximum of the reflected waves for all positions of the adjustable connection occurs at substantially the end of the short circuited stub-line towhich a transmission line or other network is connectable. The amount of overlap as well as other dimensions of the transformer may be considerably varied, and the relative dimensions which may be chosen are further described hereinafter.

The adjustment of the'transformer is carried out by providing a movable connection comprising a pair of conductors conductively connecting the corresponding conductors of the two stublines. This adjustable connection is movable lengthwise of the stub-lines and as the short circuited end of one stub-line is varied by such adjustment, the open circuited end of the other line is likewise varied but in the inverse relation. It follows, therefore, that the overall effective length of the two stub-lines always remains the same regardless of the position of the adjustable connection. When the connection is moved toward the short circuited end of the one stub, the

.otherstub, the impedance correction is reduced.

Since only one adjustment is required by my improved impedance matching transformer, it is not only highly satisfactory in matching two dissimilar impedances but may also be used in conjunction with a plurality of loads for connection to a common source of high frequency current. Thus, when a plurality of impedance lines or loads are to beconnected to a common transmission line, a separate impedance transformer may be provided for each of the loads and since only one adjustment is required for each transformer, it is a relatively simple matter to adjust the two or more transformers to reach an impedance balance at the common junction.

The impedance matching transformer of this invention is also of particular use for matching a plurality of sources of energy to a single or a plurality of loads. The transformer connection to a plurality of sources of energy may be accomplished by a step-down transformer arrangement wherein the short-circuited stub-line thereof is chosen in the order of a half wavelength. In this arrangement the amplitude of the standing waves produced by the transformer provides a reduction in the impedances at the transformer connection looking in the direction of the load, a minimum wave point occurring at the end of the half wavelength line to which the sources of energy are connected.

If more than one load is applied to the transmission line, then, in addition to the step-down transformer just described, a step-up transformer will be required for each such additional load. Thus, the plural sources of impedance lines may be matched by a single transmission line and th impedance thereof again matched to a plurality of loads.

For a better understanding of the invention, reference may be had to the following detailed description to be read in conjunction with the accompanying drawing, in which,

Fig. 1 is a schematic illustration of the stepup transformer of my invention applied to a transmission system coupling a plurality of loads to a single source of high frequency current; and

Fig. 2 shows an impedance matching transformer of my invention of the step-down type coupling a single load to a plurality of sources of high frequency current.

Referring to Fig. 1 of the drawing, I have shown tWo sources of high frequency current 5, 5 having two transmission lines 6, I and 6, 1' to which a plurality of loads Ll, L2 and L3 are adapted to be coupled by transformers If], ll and i2, respectively. Each load such as Ll may be connected by means of a transmission line 8, 9, which preferably is matched to the load, to the transformer IE3. Where it is desirable to have a common junction to the transmission line 6, I at a distance'from the transformer, a connecting line such as M, l5 may be provided in the order of a half wave or a multiple thereof between the transformer and the common junction. The transformers l0 and 12 are shown connected by lines each a wavelength long and the transformer H is shown connected by a line a half wavelength long.

Since each of the transformers In, H and I2 is identical to the other, a detailed description of one will suifice.

Referring to the transformer ID, the stub-line thereof comprises a pair of parallel conductors 20 and 21 connected together at one end by a short circuiting conductor 22. The ends 23 and 24 of the conductors 20 and 2! are connected through the connecting line H2, 5 to the common junction 33, 3|. The open circuited stubline of the transformer It! comprises two parallel spaced apart conductors 25 and 25, the ends 21 and 28 of which are adapted to be connected to the lines 8' ands of the load I. In some installations theco'nductors 25 and 25 may comprise extensions of the transmission line 8, 9.

The two stub-lines may overlap in spaced relation for about two-tenths of a wavelength, more or less. This overlapping relationship depends on the impedance characteristics of the adjustable connection between the two lines and also the length of the distance C. When these relations are properly chosen the operating results of the combined stub-lines provides maximum voltage points at the ends 23, .24 and at points a half wavelength and multiples of half wavelengths therefrom along the line I l, l5.

The adjustment of the impedance matching characteristics of the transformer is effected by a movable bracket 35 having two suitably arranged conductors 36 and 31, the conductor 36 providing conductive connection. between the conductors 20 and 25 of the two stub-lines and the conductor 31 providing conductive connection between the conductors 2i and 26. The location of this conductive connection between the two lines may be described as dividing the effective lengths of the lines between parts A and B. The distance A is the distance between the conductors of the bracket 35 and the open end of the open circuited stub-line and the distance B is the distance from the conductors of the bracket 35 to the short circuiting bar 22 of the short circuited stub-line. As the bracket 35 is moved either to the right or left, the distances A and B will be varied in inverse relation. That is to say, when the bracket 35 is moved toward the short circuited conductor 22, the distance B will be diminished and the distance A will be increased proportionally. Conversely, when the bracket 35 is adjusted in a direction toward the open end of the open circuited stub-line, the distance A will be decreased and the distance B will be increased, the overall effective length of the two stub-lines (that is, A plus B) will always remain the same. It will, therefore, be clear that the adjustments of my impedance matching transformer may be made without changing the overall effective length of the coupling.

As an illustrative example of the relative dimensions of a transformer constructed in accordance with my invention, the dimensions in the following table are those of a transformer which I caused to be constructed and which was successfully operated at megacycles. The dimensions in the table are given with respect to the parts shown in the transformer ill, Fig. 1.

Dimensions of transformers for 110 mc.

Diameter of conductors 20, 2|, 25 and and M are shown connected The tworectangularbars referred to in the table are. mounted on a'plate made; ofta composition of mica and a phenolcondensation product known as Micalex..f" The; sides: of the bars; are provided with arcuate grooves to accommodate the conductors of the stub-lines with which the bars have sliding contact.

While I have found the. foregoing dimensional relations of the transformer to operate satisfactory at 110 megacycles, I wish it understood that the invention, isrnotzrestricted to these dimensional proportions but-that: they may bezconsiderably varied depending; apparent y upon. variance of the impedance, of: certain of" the parts thereof. For example, a variationin the impedance of the movable bracket 35 may require a different dimensional relation; between. the lengths A, B on the one hand and C onthe other hand. Also, the overall distance A. plus B. plus C may be greater than a quarter wavelength. It will be understood, therefore, that the dimensions given for the llil-megacycle transformer are selected for purposes of illustration only andthat they may be varieddepending upon the wavee length and thestructural shapes and arrangements of the parts thereof.

The transformer It as above described may be adjusted by moving the bracket. 35 so as to effect the desired wave reflections and therefore vary the amplitude of the standing waves in the stubline to correct the difference between the impedance of the load LI and the source of energy supplied by the transmission line 6, T. For a plurality of loads such as Ll, L2, and L3','individual impedance matching transformers are provided for the loads and these transformers may be adjusted by moving the bracket 35 of each to such a position that the combined impedances" of the three parallel loads will balance with the characteristic impedance of the transmission line 6, I. Should, for example, each of the loads L1, L2 and L3 be 500 ohms and the characteristic impedance of the transmission line be 500 ohms, the parallel loads each should have the appearance of 1500 ohms. This may be effected by pro-per adjustment of the brackets 35 of the transformers Iii, H and I2. Should the loads Ll, L2 and L3 be dissimilar, the adjustments of the transformers l9, Hand [2 will then be correspondingly different, depending, of course, upon the particular impedance of the load associated with each transformen g In the form shown in Fig. 2 of the drawing, a plurality of sources of high frequency current 40 through suitably matched transmission lines 42 and 43 to a common junction 45 to which a load L4, which may be an antenna, is connected by a transmission-line 46, which preferably is matched to the load L4, and an impedance matching transformer 50 of an impedance step-down type.

The transformer 50 may be arranged for reciprocatable adjustment as shown in Fig. 1 or the adjustment feature may be effected in any other suitable manner. In Fig. 2, I have chosen to show the transformer 50 with a rotatable bracket 55. The short circuited stub-line 52 has a bracket engaging portion 5! thereof curved in the form of an arc of a circle about .2 wavelength long. This curved portion is connected by a portion C" the length of which may be varied from about 0.05 to about 0.25 wavelength more or less depending upon the differences, if any, in the surge impedance of the conductors of the stub-lines and the conductors of the adjustable connecting bracket '55. The open circuited stub-line 54 is curved like the portion 5| andarranged in spaced opposed relation thereto. The lengths A, B, and C correspond to the lengths A, B and C of the form shown in Fig. 1.

By adding to the short circuited stub-line 52 a quarter wavelength of line 53, the minimum voltage point of the line Will occur substantially at the junction point and this relationship renders the operation of the transformer as an impedance step-down transformation between the plural'sources of energy and the single load L4. If desired, an additional length or lengths of line in the order of a half wavelength or multiple thereof may be inserted between the line section 53 and junction points 45.

From the foregoing, it will be clear that a plurality of sources of energy may be coupled to a plurality of loads. In other" words, the loads Ll, L2, and L3 may be substituted for the load L4 by using the same transformer arrangement as illustrated in Fig. 1 to the right of the junction points 30, 3|. Such a system will then have a plurality of sources of energy having a common junction such as 45, a step-down transformer such as coupled in a transmission line between the junction 45 and the load junction 30, 3| to which a plurality of loads such as Ll, L2 and L3 are coupled by step-up transformers I0, I l and I2. While two forms of the transformer and two applications thereof are shown and described, it is recognized that many variations of the two forms together with many applications thereof are possible without departing from the invention. It will be understood, therefore, that the forms herein illustrated and described'are to be regarded as illustrative of the invention only and not as restricting the appended claims.

What I claim is:

1. An impedance matching transformer for connecting together two networks of dissimilar impedances to selectively control the amount of energy transferred between said networks while maintaining; the impedance matching, comprising a short circuited stub-line conductively associatable with one of said networks, an open circuited stub-line conductively associatable with the other of said networks, said stub lines being positioned in overlapping spaced relationship, the conductors of said stub lines being disposed to define the corners of a rectangle lying in a plane perpendicular to the stub lines with the conductors of each stub line lying in adjacent corners of said rectangle, means conductively connecting the stub-lines together, and said means being movable to vary in inverse relation the effective lengths of the two stub-lines.

2. An impedance matching transformer for connecting together two networks of dissimilar impedance to selectively control the amount of energy transferred between said networkswhile maintaining the impedance matching, comprising a short circuited stub-line conductively associatable with one of said networks, an open circuited stub-line conductively associatable with the other of said networks, the two lines being disposed in overlapping spaced relationship for a distance approaching but not equalling a quarter wavelength, means conductively connecting said lines together, and said means being movable lengthwise of said sections to vary in inverserelation the effective lengths of the two lines.

3. An impedance matching transformer for connecting together two networks of dissimilar impedance comprising a short circuited stub-line,

an open circuited stub-line conductively associatable with one of said networks, the stub-lines being disposed in overlapping spaced relationship. a line a quarter wavelength connecting the short circuited stub to the other of said net works, means conductively connecting the stublines together, and said means being movalle lengthwise of said lines to vary in inverse relation the lengths of the two lines.

4. An impedance matching transformer for connecting together two networks of nilar impedance to selectively control-the amount of energy transferred between said networks while maintaining the impedance matching, comprising a two-conductor section having one end thereof short circuited and the other end connectable to one of said networks, a second twoconductor section having one end open circuited and the other end thereof connectable to the other of said networks, the sections being in spaced apart, parallel relation for at least a portion of their lengths with the conductors being disposed to define a rectangle in a plane perpendicular to the axis of the conductors and with the conductors of each section lying in adjacent corn rs of the rectangle so formed, means including a pair of conductors conductively connecting the corresponding conductors of said sections, said means being movable lengthwise of said sections to vary the impedance matching char acteristics thereof while maintaining substantially constant the combined overall efiective lengths of the sections.

5. A step-up impedance matching transformer for connecting together two networks of dissimilar impedance to selectivel control the amount of energy transferred between said networks while maintaining the impedance matching, comprising a two-conductor section in the order of a quarter wavelength or odd multiple thereof having one end thereof short circuited and the other end connectable to one of said networks, a second two-conductor section in the order of a quarter wavelength having one end open circuited and the other end thereof connectable to the other of said networks, the sections being in spaced apart, parallel relation for a portion but not all of their lengths, means including a pair of conductors conductively connecting the corresponding conductorsof said sections, and said means being movable lengthwise of said sections to vary the points of conduction between the corresponding conductors of said sections.

6. A step-down impedance matching transformer for connecting together two networks of dissimilar impedance comprising a two-conductor section in the order of a half wavelength or multiple thereof having one end thereof short circuited and the other end connectable to one of said networks, a second two-conductor section having one end open circuited and the other end thereof oonnectable to the other of said networks, the sections being in spaced apart, parallel relation for a portion of a quarter wavelength so that the four conductors form the corners of a rectangle lying in a plane perpendicular to the axis of the sections, with the conductors of each section being disposed in adjacent corners of the rectangle so formed, means including a pair of conductors conductively connecting the corresponding conductors of said sections, and said means being movable lengthwise of said sections to vary the points of conduction between the corresponding conductors of said sections.

"7. A step-up impedance matching transformer for connecting together two networks of dissimilar impedance comprising a two-conductor section in the order of at least a quarter wavelength having one end thereof short circuited and the other end connectable to one of said networks, a second two-conductor section having one end open circuited and the other end thereof connectable to the other of said networks, the sections being in spaced apart, parallel relation for about two tenths wavelength, and means including a pair of conductors about one twentieth wavelength conductively connecting the corresponding conductors of said sections, and said means being movable lengthwise of said sections to vary the points of conduction between the corresponding conductors of said sections.

8. In an electrical transmission system having a plurality of sources of high frequency energy, a transmission line and a load therefor; the combination therewith of a step-down impedance matching transformer to connect said transmission line to the common junction of said two sources of energy, said transformer comprising a two-conductor section connected at one end thereof to said junction and having the other end thereof short circuited, a second two-conductor section connected at one end thereof to said load and having the other end thereof open circuited, means including a pair of conductors conductively connecting the corresponding conductors of said sections, and said means being movable lengthwise of said sections.

9, In an electrical transmission system having a, plurality of sources of high frequency energy, a plurality of loads and a transmission line to connect the loads to the common junction of said sources; the combination therewith of a stepdown impedance matching transformer between said line and said junction and a step-up impedance matching transformer for each of said loads, each of the step-down and step-up transformers comprising a short circuited stub-line, an open circuited stub-line, means conductively connecting together said lines, said means being movable to vary in inverse relation the effective lengths of the two stub-lines.

CHESTER B. WATTS, J R. 

